1. Field of the Invention
This invention related to signal converters, and more particular to signal converters employing a quad diode race or bridge.
2. Description of the Prior Art
Representative of the techniques used in the prior art for achieving a doubly balanced microwave mixer is the patent of Neuf, U.S. Pat. No. 3,652,941. Among other things, Neuf teaches a doubly balanced mixer using two tapered microstrip constructed baluns for connection to a quad diode bridge. Electrically, a radio-frequency (RF) signal is coupled by one of the baluns to two of the corners of the bridge, and a local oscillator (LO) signal is coupled by the other balun to the other two corners of the bridge. Two pairs of RF chokes are used to remove the IF output signal from the diode bridge and to provide a dc return path.
Physically, the Neuf mixer is constructed with the diode bridge mounted in a hole in a substrate on which the microstrip baluns are formed. Connections to the diode bridge are achieved with some effort using specially placed leads to connect to the microstrip leads on opposite surfaces of the substrate adjacent the mounting hole where the microstrip leads terminate. The need for such multiple connections on opposite surfaces of the substrate is necessitated, in part, by the constraint (heretofore considered necessary) that the RF and LO signals be applied to the diode bridge in a balanced or floating state; in other words, that balun elements be used to couple the respective input signals to the diode bridge.
This seeming constraint dictating inputs to a quad diode bridge is further illustrated by the recently issued patent to Hill, U.S. Pat. No. 4,032,850, which, like Neuf and others, utilizes baluns to connect both the RF and LO inputs to a diode bridge.
Various other microstrip and stripline construction techniques applicable to microwave mixers are taught in the U.S. Pat. Nos. to Carpenter et al., 3,634,768, Vendelin, 3,571,722; Hunton et al., 3,678,395; Shinkawa et al., 4,008,438; and Shinkawa et al., 4,031,472.
Finally, a balanced mixer is shown by Tenenholtz in U.S. Pat. No. 3,706,042 using a pair of quadrature hybrid mixers. In the Tenenholtz mixer, the signals are coupled to the quadrature hybrid mixers by first and second quadrature hybrid elements in a balanced configuration. It should be noted that the diodes used are configured in a star arrangement having a common interconnection point, but nevertheless, a balanced input for both signals is deemed necessary.